The background of the invention is described below by using a silicon wafer as an object to be cleaned.
Cleaning of a silicon wafer in the semiconductor industry is one of the most-important semiconductor producing processes.
That is, a lot of impurity particles are attached on a silicon wafer. Therefore, if a device is formed on the silicon wafer without removing the particles, only a device having bad characteristics can be obtained. Therefore, a silicon wafer is generally cleaned with demineralized water to remove impurities.
The following are objects particularly affecting a semiconductor device on the surface of a wafer.
(1) Particles PA1 (2) Organic contaminants PA1 (3) Metallic impurities PA1 (4) Native oxides PA1 (5) Surface micro roughness PA1 (6) Molecules adsorbed on the surface PA1 Cleaning with H.sub.2 SO.sub.4, H.sub.2 O.sub.2, and ultrapure water PA1 Cleaning with ultrapure water PA1 Cleaning with HF, H.sub.2 O.sub.2, and ultrapure water PA1 Cleaning with ultrapure water PA1 Cleaning with NH.sub.4 OH, H.sub.2 O.sub.2, and ultrapure water PA1 Cleaning with hot ultrapure water PA1 Cleaning with HF, H.sub.2 O.sub.2, ultrapure water PA1 Cleaning with ultrapure water PA1 Drying PA1 a cleaning bath having a movable cover at its top so that the apparatus can be sealed when closing the cover; PA1 object-to-be-cleaned holding means for holding an object to be cleaned in the cleaning bath; PA1 rotating means for rotating the object-to-be-cleaned holding means; PA1 gas introducing means for introducing a gas into the cleaning bath; PA1 a first nozzle for spraying a first chemical solution onto the surface of the object to be cleaned held by the object-to-be-cleaned holding means; PA1 a second nozzle for spraying a second chemical solution onto the surface of the object to be cleaned held by the object-to-be-cleaned holding means; PA1 a third nozzle for spraying the first chemical solution onto the back of the object to be cleaned held by the object-to-be-cleaned holding means; PA1 a fourth nozzle for spraying the second chemical solution onto the back of the object to be cleaned held by the object-to-be-cleaned holding means; PA1 a fifth nozzle for spraying ultrapure water onto the surface of the object to be leaned held by the object-to-be-cleaned holding means; PA1 a sixth nozzle for spraying ultrapure water onto the back of the object to be cleaned held by the object-to-be-cleaned holding means; PA1 a chemical-solution feed line connected to the first to the fourth nozzles respectively; PA1 an external chemical-solution feeder for feeding a chemical solution, connected to each chemical-solution feed line; PA1 an ultrapure water feed line connected to the fifth and sixth nozzles; PA1 ozone adding means for selectively adding ozone to ultrapure water; and PA1 a drainage system for perfectly separating waste liquids after cleaning. PA1 &lt;1&gt; Ozone-added cleaning with ultrapure water PA1 Cleaning with ultrapure water PA1 &lt;2&gt; Cleaning with HF, H.sub.2 O.sub.2, and ultrapure water PA1 Cleaning with ultrapure water PA1 &lt;3&gt; Cleaning with NH.sub.4 OH, H.sub.2 O.sub.2, and ultrapure water PA1 Cleaning with ultrapure water PA1 Cleaning with hot ultrapure water PA1 Cleaning with ultrapure water PA1 &lt;4&gt; Cleaning with HF, H.sub.2 O.sub.2, and ultrapure water PA1 Cleaning with ultrapure water
However, only particles can be removed by demineralized water but native oxides formed on the surface cannot be removed. Moreover, it is difficult to remove fine particles among particles by demineralized water.
Therefore, cleaning is performed by using various types of chemical solutions. One of them is RCA cleaning.
However, the RCA cleaning is not greatly improved compared with the RCA cleaning in its early stages. Therefore, in fact, cleaning is performed in many processes for a long time.
The RCA cleaning removes organic contaminants from the substrate surface by oxidizing them. Its treatment processes are roughly shown below.